[enrichments] Add enrichment logic for `user_agent.*`

[lahsivjar]

These sets of attributes are not always set by the OTel SDKs but are required by the UI. The below OTTL statements can be used as an algorithm for populating these fields based on stable OTel semconv:

transform/user_agent:
    trace_statements:
      - merge_maps(span.cache, UserAgent(span.attributes["user_agent.original"]), "upsert") where span.attributes["user_agent.original"] != nil
      - set(span.attributes["user_agent.name"], span.cache["user_agent.name"])
      - set(span.attributes["user_agent.version"], span.cache["user_agent.version"])
      - set(span.attributes["url.full"], Concat([span.attributes["url.scheme"], "://", span.attributes["server.address"]], ""))
      - set(span.attributes["url.full"], Concat([span.attributes["url.full"], span.attributes["server.port"]], ":")) where span.attributes["server.port"] != nil
      - set(span.attributes["url.full"], Concat([span.attributes["url.full"], span.attributes["url.path"]], "")) where span.attributes["url.path"] != nil
      - set(span.attributes["url.full"], Concat([span.attributes["url.full"], span.attributes["url.query"]], "?")) where span.attributes["url.query"] != nil

In the above OTTL statements, the UserAgent converter func uses https://github.com/ua-parser/uap-go which can be used by this library to do the same enrichment.

Based on recent developments, the url.full will be built in the UI so we only need to do the user_agent bit in the opentelemetry lib.